1. Field of the Invention
The present invention relates to a computer touch panel input device, and more specifically, to a method and apparatus for avoiding pressing inaccuracies in the touch panel.
2. Description of the Prior Art
A touch pad is a tool for data communication applied in different portable electrical products like a personal data assistance (PDA), a mobile phone, or a notebook. A touch pad integrating input and output functions on a single panel combined with functions of a keyboard, a mouse, and hand-writing can increase efficiency of operations.
Several different technologies are applied in a recently developing touch pad industry, wherein a resistive type touch pad is the commonest one in the market. On a resistive panel of a touch pad, layouts are distributed on an ITO glass and an ITO film according to X and Y dimensions, a dot spacer is arranged in between an upper and a bottom transparent electrode wherein when the upper transparent electrode is pressed by a finger, a pen, or other similar object, the bottom electrodes can make contact indirectly with the upper electrodes. Additionally, different voltage drops differentiated by resistors are used to generate corresponding parameters for calculating positions being pressed on the panel in X-Y dimensions. Please refer to FIG. 1. Illustrated in FIG. 1 is a block diagram of a conventional touch pad 10. The touch pad 10 comprises a panel 12, a control module 14, and a processor 16. The control module 14 is electrically connected to the panel 12, and comprises an analog-to-digital converter (ADC) 20 and a touch apparatus 22. The processor 16 controls operations of the touch pad 10. Additionally, the touch pad 10 comprises an operating system 18. When the panel 12 is pressed, the control module 14 can detect voltage variations on the panel 12 and use the touch apparatus 22 for generating a trigger signal IRQ to alert the processor 16 to read data. Then, the processor 16 will output commands to the control module 14 for reading voltage values on X and Y dimensions respectively, wherein the control module 14 will connect a point X+ to a voltage VCC, connect a point X− to a ground for generating a voltage drop with value of VCC between a resistor RX1 and RX2. Thus, a voltage drop on the X dimension can be detected at a point Y+. Similarly, at a point X+, a voltage drop on the Y dimension can be detected too. Neglecting any leaking current at the points X+ and Y+, the voltage drops can be represented as:
          ⁢      {                  X        ⁢                                  ⁢        dimension        ⁢                                  ⁢                  :                ⁢                                  ⁢        Vx            =                        VCC          ×                      RX2            /                          (                              RX1                +                RX2                            )                                ⁢                                          ⁢                                          ⁢          Y          ⁢                                          ⁢          dimension          ⁢                                          ⁢                      :                    ⁢                                          ⁢          Vy                =                  VCC          ×                      RY2            /                          (                              RY1                +                RY2                            )                                          
The analog voltage signals of voltage values on the X and Y dimensions generated from the panel 12 will be transformed to corresponding digital signals by the analog-to-digital converter 20 to the processor 12 at which positions being pressed on the panel 12 can be determined. Thus, the touch pad 10 can determine positions and tracks of a finger or a pen by detecting voltage variations. Please refer to FIG. 2. Illustrated in FIG. 2 is a flowchart of operations of the touch pad 10. After being pressed, the panel 12 will generate a trigger signal IRQ to alert the processor 16. Getting signals regarding to positions, the processor 16 will report to the operating system 18. If the panel 12 is being pressed continuously, the processor 16 will report associated signals to the operating system 18 successively. Thus, two points will be linked as a line, and several points will be linked as a graph until the finger or the pen is removed from the surface of the panel 12.
Many technologies relating to touch pads are disclosed. In U.S. Pat. No. 5,898,426, “Touch panel input device”, Kim and et al. disclose a touch pad structure similar to the touch pad 10 illustrated in FIG. 1 with an advantage of being easy to operate. In U.S. Pat. No. 5,670,755, “Information input apparatus having functions of both touch panel and digitizer, and driving method thereof”, Kwon and et al. also disclose a similar touch pad further including a stylus pen and a converter to achieve advantages of increasing pressing stability and making the touch pad operate like a digitizer. In U.S. Pat. No. 6,088,024, “Touch panel and method for detecting a pressed position on a touch panel”, Yamagata and et al. disclose a touch pad, divided into a display region with functions of a conventional touch pad and a non-display region with functions of a keyboard applied with a switch circuit for a user to make commands or perform hand-writing on the touch pad. However, the structure and arrangement of the touch pad disclosed in the U.S. Pat. No. 6,088,024 is still similar to the other conventional resistive touch pads. Additionally, in U.S. Pat. No. 6,259,597, “Portable electronic device”, Anzai and et al. disclose a portable device combined with a fingertip tablet function, a digitizer function by a pen, and a conventional keyboard. Such multiple function combination is truly the development point of the industry.
Basic arrangement and structure is very similar in the above-mentioned touch pads. However, there are still some obstacles to overcome in a resistive touch pad, such as transparent rates, sustainability, and pressing inaccuracies. The problem of pressing inaccuracies is the most vital concern to a user. During operations of a touch pad, at any moment when a touch pad is pressed with a pen, a finger, or similar object, or such pressing objects are removed from the touch pad, contact resistance will be increased because of insufficient pressing pressure, which will influence results detected at observing points. Please refer to FIG. 1 again. As the leaking current on observing point Y+ is small and a value of a series resistance RY1 is also small, voltage drops can be neglected and the voltage value detected on the X dimension will remain Vx. However, if the contact resistance is increased, voltage drops will have greater effect such that the voltage value detected on the X dimension will be less than Vx. Similarly, the voltage value detected on the Y dimension will be less than Vy. The situation will result in unexpected error dots on screen of the touch pad. During successive writing operations, it is highly possible to have imperfect contacts because of instable pressing pressures. Thus, the trigger signal IRQ generated by the control module 14 will not stay at a low potential so that the system will erroneously determine that the pen, the finger, or similar objects has been removed from the panel so as to have a line-breaking problem.
Furthermore, the panel 12 of the touch pad 10 comprises an ITO glass layer and an ITO film layer fixed in place by a seal around the edges of the panel 12. Please refer to FIG. 3. Illustrated in FIG. 3 is a cross sectional diagram of the panel 12 illustrated in FIG. 1. According to basic principles of physics, as the seal layer is applied to fix the panel 12, the touching strength used to stabilize the trigger signal IRQ at a margin domain is larger than that at a central domain. Therefore, it is easier to have error dots or line-breaking problems near the edges of the panel 12. For example, it takes only 80 g at the central domain to stabilize generations of the trigger signal IRQ, but it takes about 150 g at the margin domain to stabilize the trigger signal IRQ. Therefore, at the margin domain of the panel 12, line-breaking problems tend to frequently occur and pressing inaccuracies are more than at the central domain of the panel 12.
Most of the technologies developed recently are focusing on structural aspects of a touch pad. Take a resistive touch pad for example; a touch pad having five wires with advantages in durability and a touch pad having six wires with advantages of avoiding radiation and noise have been developed in recent years. However, there is still no easy solution for the pressing inaccuracies problem in the industry. A conventional resistive touch pad structure and arrangement complemented with some modifications to software processing and hardware design could alleviate the pressing inaccuracies problem, which would be very helpful to the industry.